radius

/ˈreɪdiəs/

/ˈreɪdiəs/

Other forms: radii; radiuses

If you're a detective working a crime investigation, you might be told to "search over a one-mile radius," meaning, scope out everything that's within one mile of the crime scene.

The radius of a circle is the distance from its center to the circumference, and if you are working on your geometry homework, or designing anything circular, you'll be writing down a little "r" quite frequently, to stand for "radius." It's also the name of one of the bones in your forearm.

Definitions of radius

1. noun

   a straight line from the center to the perimeter of a circle (or from the center to the surface of a sphere)
   type of:

   straight line

   a line traced by a point traveling in a constant direction; a line of zero curvature
2. noun

   support consisting of a radial member of a wheel joining the hub to the rim
   synonyms: spoke, wheel spoke

   type of:

   support

   any device that bears the weight of another thing
3. noun

   the length of a line segment between the center and circumference of a circle or sphere
   synonyms: r

   types:

   semidiameter

   the apparent radius of a celestial body when viewed as a disc from the earth

   radius of curvature

   the radius of the circle of curvature; the absolute value of the reciprocal of the curvature of a curve at a given point

   type of:

   length

   the linear extent in space from one end to the other; the longest dimension of something that is fixed in place
4. noun

   a circular region whose area is indicated by the length of its radius
   “they located it within a radius of 2 miles”

   type of:

   part, region

   the extended spatial location of something
5. noun

   the outer and slightly shorter of the two bones of the human forearm
   type of:

   arm bone

   a bone in the arm